1. Field of the Invention
The present invention relates to an electric filter and a duplexer using the same and, more particularly, to an electric filter with a piezoelectric resonator using a bulk wave propagating in a piezoelectric film, and a duplexer using the electric filter.
2. Related Background of the Invention
Piezoelectric resonators with advantage for size reduction are used, for example, in duplexers and electric filters mounted on portable, wireless communication devices.
The electric filters in personal communication systems (PCS) using the duplexer are demanded to achieve the pass bandwidth of 60 MHz in the 1.9 GHz band. It is difficult for an electric filter using a conventional piezoelectric to satisfy this specification by itself. There is thus a known band-increasing technology of extending the pass bandwidth by use of an inductor (L), as described in Japanese Patent Application Laid-Open No. 2001-244704.